The present invention relates to a system for the alkylation of an olefin with an isoparaffin utilizing an acidic catalyst mixture. In another aspect, this invention relates to a system useful for handling fluids in an alkylation process.
The use of catalytic alkylation processes to produce branched hydrocarbons having properties that are suitable for use as gasoline blending components is well known in the art. Generally, the alkylation of olefins by saturated hydrocarbons, such as isoparaffins, is accomplished by contacting the reactants with an acid catalyst to form a reaction mixture, settling the reaction mixture to separate the catalyst from the hydrocarbons, thereby forming a catalyst phase and a hydrocarbon phase. The hydrocarbon phase is further separated, for example, by fractionation, to recover the separate product streams. Normally, the hydrocarbon phase of the alkylation process contains hydrocarbons having three to ten carbon atoms per molecule. In order to have the highest quality gasoline blending stock, it is preferred for the alkylate hydrocarbons formed in the alkylation process to be highly branched and contain seven to nine carbon atoms per molecule.
The safe handling and storage of alkylation catalyst has long been a concern to those operating alkylation units. Refiners have typically employed catalyst receiving vessel(s) located below a settler vessel which is/are suitable for receiving the alkylation catalyst volume contained in the alkylation unit and/or suitable for holding make-up catalyst needed to periodically recharge the alkylation process as catalyst is consumed during operation. These catalyst receiving vessels have typically been operated under a blanket of non-condensible gas such as nitrogen, and non-condensible gases can otherwise enter the catalyst receiving vessel during transfer operations. These catalyst receiving vessels are usually vented to a flare, via a treating system wherein acid is neutralized, during a catalyst transfer from the process unit or during a fresh catalyst receiving operation. Such venting is preferably minimized due to environmental and economical considerations. One problem with the current catalyst receiving vessel system is that as the pressure in the catalyst receiving vessel increases due to the addition of catalyst to the vessel containing non-condensible gas, the motive force for transferring catalyst diminishes. While this is not necessarily detrimental to a fresh catalyst loading operation, it is a significant safety concern for the transfer of catalyst from the process (usually reserved for emergency situations) wherein faster transfer times are preferred.
Therefore, development of an improved system for transferring alkylation catalyst to a catalyst receiving vessel would be a significant contribution to the art.